Bra Size International Converter & Sister Size Calculator
HOTConvert bra sizes across US/UK, Korea/Japan, EU, France, and Australia based on snug underbust and overbust, with custom Sister Size recommendations.
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(CLS Prevention Active · Zero Shift)International Bra Size Converter & Sister Size Guide
The International Bra Size Converter & Sister Size Calculator calculates accurate intimate apparel measurements across US/UK (34B), Korea/Japan (75B), European EU (75B), French (90B), and Australian (12B) sizing systems.
By evaluating underbust band perimeter and full overbust cup dimensions, it translates measurements into international equivalents and generates Sister Sizes for custom band-to-cup tension calibration.
Clinical studies show that over 80% of women wear incorrect bra sizes, resulting in mastalgia, trapezius spasm, underwire pinching, and lateral tissue displacement.
Overbust-Underbust Delta & Cup Volume Conservation
Cup volume is conserved across sister sizes by counter-shifting band and cup parameters.
32C, 34B, and 36A all encapsulate identical breast tissue volume. If a 34B cup fits well but pinches your ribs, 36A relieves pressure without cup gaping.
👉 Baseline size is US 34B (KR/EU 75B). If the band feels tight, sister size 36A provides equal volume with greater ribcage comfort.
International Bra Size Conversion Matrix & Cup Concordance
Equivalents across US/UK, Asian, EU, French, and Australian sizing systems
| Overbust - Underbust Delta | KR/JP Cup | US/UK Cup | Underbust Measurement | KR/EU Band | US/UK Band (in) | France Band | Australia Band |
|---|---|---|---|---|---|---|---|
| < 10.0 cm (< 4.0 in) | AA | AA | 63 - 67 cm (25-26 in) | 65 | 30 | 80 | 8 |
| 10.0 - 12.5 cm (4-5 in) | A | A | 68 - 72 cm (27-28 in) | 70 | 32 | 85 | 10 |
| 12.5 - 15.0 cm (5-6 in) | B | B | 73 - 77 cm (29-30 in) | 75 | 34 | 90 | 12 |
| 15.0 - 17.5 cm (6-7 in) | C | C | 78 - 82 cm (31-32 in) | 80 | 36 | 95 | 14 |
| 17.5 - 20.0 cm (7-8 in) | D | D | 83 - 87 cm (33-34 in) | 85 | 38 | 100 | 16 |
| 20.0 - 22.5 cm (8-9 in) | E | DD (E) | 88 - 92 cm (35-36 in) | 90 | 40 | 105 | 18 |
| 22.5 - 25.0 cm (9-10 in) | F | DDD (F) | 93 - 97 cm (37-38 in) | 95 | 42 | 110 | 20 |
| 25.0 - 27.5 cm (10-11 in) | G | G | 98 - 102 cm (39-40 in) | 100 | 44 | 115 | 22 |
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(CLS Prevention Active · Zero Shift)How to Use
11. Measure Snug Underbust
Measure directly beneath breast tissue against the ribcage with relaxed breathing (in cm or inches).
22. Measure Full Overbust
Lean forward 45 degrees and measure across the fullest part of the bust (nipple apex) without compressing tissue.
33. Review International Labeling
View your exact size across US/UK, Asian, European, French, and Australian standards.
44. Check Sister Size Alternatives
Review Sister Sizes (band up/cup down or band down/cup up) to adjust ribcage tightness.
Online Lingerie Shopping & Fitting Trouble-Shooting
Real-world size translation and adjustments
A customer wearing an Asian 75D converting to a US 34D for Victoria's Secret or Calvin Klein
Transitioning from a painful 34B to sister size 36A to relieve costal cartilage pressure while keeping cup fill intact
Sizing down to sister size 32C for heavy breast tissue support during evening wear
Updating from 36B to 32D after dropping 6 cm of underbust circumference, preserving breast cup tissue in a firmer band
💡 Professional Lingerie Fitting Guidelines
Support originates from the band, not shoulder straps; if your back band rides up toward your neck, size down in the band.
New bras should fit snugly on the outer hook so you can adjust inward as the elastane naturally relaxes over time.
Leaning forward 45 degrees prevents soft or post-nursing breast tissue from flattening against the chest wall.
⚠️ Common Pitfalls & Mistakes to Avoid
Frequently Asked Questions (FAQ)
Expert answers to the most frequently asked questions and edge cases.
Sister Sizes are alternate bra sizes that share the exact same physical cup volume despite having different band circumferences. When you increase the band size by one step, you must decrease the cup letter by one step to preserve volume (e.g., 32C, 34B, and 36A all hold identical breast volume). If your cup fits nicely but the band pinches your ribcage, trying your sister size up (36A) provides comfort without empty cups.
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